Tamron 28 to 300mm Lens
How Compact Can You Get
If you go way back you remember
the first telephoto zoom lenses as heavy, ungainly things that were
often more trouble than they were worth. Travel a bit ahead in time
and check out the wide-to-tele zooms, and you get the same thing, with
all sorts of problems that were not quite solved at numerous focal length
settings. In the here and now all that has changed, especially when
you consider the latest XR series lens from Tamron--the 28-300mm
f/3.5-6.3. When we spell out the specs you might not believe them. The
lens is 3.3" in length and weighs 13.5 oz and has a filter diameter
of 62mm. The minimum focusing distance is 19.29, throughout the entire
focal length range.
In The Field
The Alphabet Soup Of Tamron Lens Technology
XR: The namesake of
the lens line stands for Extra Refractive Index, which is a numerical
expression that compares the speed of light in a transparent medium, such
as glass, with the speed of light in the air. The higher the number the
thinner a given element. Extra Refractive Index glass is said to bend
light more effectively than normal or lower refractive index glass and
can compensate for specific aberrations within an optical design.
Benefits: Shortens length of the entire optical system; shorter distance from the diaphragm to the front surface of the objective lens; lessens diameter of the front element; smaller overall lens diameter; smaller lens and minimal aberration.
ASL: This stands for
aspherical elements, and Tamron has developed a process that has allowed
for the mass production of aspherics they call Hybrid Aspherical.
LD & AD: Low Dispersion
(LD) elements are made from special glass with extremely low dispersion
indices that separate or refract a ray of light into rainbow colors. Chromatic
aberration is a form of optical noise that reduces sharpness and can plague
telephoto and zoom telephoto lenses. AD (Anomalous Dispersion) glass is
a special optical glass that delivers an abnormally large partial dispersion
ratio, the amount of dispersion at a given wavelength range within visible
ADAH: This stands for
"Anomalous Dispersion-Hybrid Aspherical," the manufacturing
method of adhering a specially treated aspherical layer to the finished
AD glass element.
ZL: The Zoom Lock can
be activated when the lens is at the 28mm focal length setting.
BBAR: A thin dielectric
or metallic film applied to the lens.
IF: Internal Focusing
enables focusing of the lens without changing its length. All internal
optical movement is limited to the interior of the non-extending lens
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